Telescoping support with double acting piston and latch and retaining means

ABSTRACT

A telescoping support such as a mast or boom employs a number of separate telescoping sections which fit one inside the other, with the outermost section being secured to a base. A double acting piston is situated completely inside the innermost section, with the piston rod being secured to the base and the piston cylinder arranged to reciprocate up and down within that section. On the upstroke of the cylinder, a hook mounted thereon engages a fixture located near the bottom of the innermost section. The cylinder hitches up the mast section, whereupon the fixture latches onto a retainer near the top of the next outer mast section. The cylinder then returns to its lowermost position and commences a second upstroke. Another hook engages a similar fixture near the bottom of the next outer mast section so that that section is lifted up until the fixture thereon latches onto the top of the third outer mast section. Again, the cylinder returns to its lowermost position and the process is repeated with the cylinder reciprocating up and down and each time hitching up the next outer mast section as well as all those supported by it until the mast is fully extended with all its movable sections being supported by the outermost section of the mast. The lower the mast, the same procedure is followed in reverse until all mast sections are recovered.

O Hate States Patent Zebuhr [54] TELESCOPING SUPPORT WITH DOUBLE ACTING PISTON AND LATCH AND RETAINING MEANS [72] Inventor: William Henry Zebuhr, Nashua,

[731 Sigma San r ss siat alysa..N shaat [22] Filed: Oct. 23, 1970 [21] App1.No.: 83,564

[52] 11.8. C1. ..52/115, 52/114, 343/883, 343/902 [51] Int. Cl. ..E04h 12/34 [58] Field of Search ..52/ll1,115,117,118,123, 52/114, 632; 92/51, 59, 167, 169; 182/2; 343/883, 901, 902

[56] References Cited UNITED STATES PATENTS 1,325,053 12/1919 Steidle ..52/115 2,173,095 9/1939 Byrne ..343/902 2,708,493 5/1955 Badertscher etal ..52/115 2,715,954 8/1955 Rowan ..52/115 2,858,154 10/1958 Johansson ..52/632 2,888,111 5/1959 Evans ..52/114 3,147,829 9/1964 Johnson etal ..52/115 3,361,456 l/l968 Durand ..52/632 3,367,632 2/1968 Vail ..52/118 3,464,169 9/1969 Potain ..52/123 3,546,831 12/1970 Romo et a1. .......52/118 3,572,467 3/197 1 Hall ..182/2 FOREIGN PATENTS OR APPLICATIONS 970,879 9/1964 Great Britain ..'...52/l l 1 Primary Examiner-F rank L. Abbott Assistant Examiner-Leslie A. Braun Att0mey-Louis Etlinger [57] ABSTRACT A telescoping support such as a mast or boom employs a number of separate telescoping sections which fit one inside the other, with the outermost section being secured to a base. A double acting piston is situated completely inside the innermost section, with the piston rod being secured to the base and the piston cylinder arranged to reciprocate up and down within that section. On the upstroke of the cylinder, a hook mounted thereon engages a fixture located near the bottom of the innermost section. The cylinder hitches up the mast section, whereupon the fixture latches onto a retainer near the top of the next outer mast section. The cylinder then returns to its lowermost position and commences a second upstroke. Another hook engages a similar fixture near the bottom of the next outer mast section so that that section is lifted up until the fixture thereon latches onto the top of the third outer mast section. Again, the cylinder returns to its lowermost position and the process is repeated with the cylinder reciprocating up and down and each time hitching up the next outer mast section as well as all those supported by it until the mast is fully extended with all its movable sections being supported by the o tei 'most s ction of he mast.

e ower t e mast, e same procedure is followed in reverse until all mast sections are recovered.

34 C la in s,17 Drawing Figures Sept. 5, 1972 United States Patent Zebuhr P'A'TENTEDSEP 51m SHEET 1 0F 5 REGULATED AIR SOURCE INVENTOR WILLIAM H. ZEBUHR ATTORNEY PATENTIZDSEP 1m 3.688.455

SHEET 2 0F 5 FIG. 2D FIGZE FIG. 2C

FIGZB FIGZA IOQ lob

INVENTOR WILLIAM H. ZEBUHR ATTO NEY PATENTEUSEP 51912 SHEET 3 BF 5 INVENTOR WILLIAM H. ZEBUHR.

ATTORNEY PAIENTEDSEP 51 saw u or 5 r711 ED 48 0 FIG, 4

INVENTO WILLIAM H. ZEBUHR TTORN Y PATENTEDSEP sma 3.688.455

SHEET 5 0F 5 INVENTOR WILLIAM H. ZEBUHR ATTORNEY TELESCOPING SUPPORT WITH DOUBLE ACTING PISTON AND LATCH AND RETAINING MEANS The invention herein described was made in the course of or under a contract with the Department of the Army.

BACKGROUND OF THE INVENTION This invention relates to a telescoping support such as a mast or boom. It has wide application, particularly as a support for a radio or television antenna in those situations where it is necessary to raise and lower the antenna quickly or with great frequency.

There are a number of conventional telescoping masts and booms which can be extended and retracted automatically. In a typical arrangement, the mast sections are connected together so that the entire mast is, in essence, an extensible, fluidtight enclosure. When air is introduced into the mast, the mast sections are pushed out. That type is normally held in its extended condition either by air pressure or by latches which lock the sections in their extended positions. A variation on that basic mast employs a telescoping lifting member or jack which fits inside the mast and which can be extended by air or other means to the full height of the mast so as to hoist up the telescoping mast sections.

These prior masts all have the same drawbacks in that they require special sliding seals and/or valves between the telescoping sections to maintain the air pressure in the mast. Sometimes leaks develop in the seals and valves which prevent the masts from operating properly. These prior supports also tend to be relatively expensive to make and maintain and they have a relatively short life.

It has also been proposed to construct an extensible mast using a single inflatable bag. However, the bag tends to squirm to such an extent that it is difficult to control the bag so that it properly supports the antenna or other load.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved telescoping support which can be raised and lowered automatically.

Another object of the invention is to provide a telescoping support which is operated pneumatically yet requires no special seals or valves between telescoping sections.

A further object of the invention is to provide a support composed of a number of telescoping sections which can be raised and lowered automatically by a mechanism situated entirely in the lowermost support section.

Yet another object of the invention is to provide an improved, extendible mast for antennas and the like which can be automatically raised and lowered in a minimum amount of time.

Another object of the invention is to provide an automatic, extendible and retractable mast which can operate properly for a long period of time with minimum maintenance.

Yet another object of the invention is to provide a pneumatically operated extendible mast which does not have to be pressurized in use.

A further object is to provide an extendible support composed of telescoping sections which are retained in their extended positions by improved releasable latches.

Other objects will in part, be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts and will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

In general, the mast is composed of a number of generally cylindrical sections which fit one inside the other when the mast is retracted and which can telescope out when the mast is extended. The antenna or other load is connected to the innermost or first section and the outermost or last section is secured to a base.

A double-acting ram including a cylinder, a piston and a piston rod is mounted inside the first mast section. The piston rod is connected to the base and the cylinder is free to reciprocate up and down when air is supplied to one end or the other of the cylinder. The stroke of the cylinder is slightly less than the length of the outermost or last mast section.

The cylinder carries a pair of hooks which are biased outwardly. On the first upstroke of the cylinder after the air is turned on, one of these hooks engages a rotary spider mounted near the bottom of the first mast section and to be described in detail later. That section is thus carried along with the cylinder and slides upwards within the next outer or second section.

When the first section reaches its upper limit of travel relative to the second section, a spring loaded latch engages a retainer situated near the top of the second mast section thereby locking the first section in its extended position atop the second section.

The cylinder immediately returns to its lowermost position and commences its second upstroke. The other hook thereon engages a similar rotary spider situated near the bottom of the second mast section. As the cylinder moves upwards, that section is hitched up within the next outer, i. e., third, mast section. When the second section reaches its upper limit of travel relative to the third section, a latch which engages a retainer near the top of the third section is released. Thus, the second section is mechanically locked in its extended position relative to the third section. The cylinder then returns to its lowermost position.

The cylinder continues to reciprocate up and down in this fashion hitching up each successive mast section (as well as all those supported by it). Each section is, in turn, locked in place atop the next outer section until the mast is fully extended with all of the sections supported by the outermost or last mast section. The cylinder then returns to its lowermost position and the air supply to the cylinder is cut off.

If needed, suitable stays can be secured to the mast and anchored to the ground to help support it and prevent it from swaying in the wind.

When it is desired to retract the mast, the same procedure is followed. That is, air is again supplied to the cylinder so that it reciprocates up and down. When the cylinder nears its upper limit of travel, one of the outwardly biased hooks thereon engages the spider on the next outermost mast section in a manner to be described later. Continued upward movement of the cylinder causes the hook to rotate the spider so that it retracts the latch from the retainer in the outermost section. Thus, when the cylinder moves downwards, it lowers the next outermost mast section (as well as all those sections supported by it) toward the base. Once the next outermost section bottoms on the base, continued downward movement of the cylinder rotates the spider so that it releases the latch which then engages in a retainer near the bottom of the outermost section, thereby locking the next outermost section in the down position. Then the cylinder moves upwardly again to retrieve the third outermost mast section in much the same way. This process continues until all of the mast sections are again nested within the outermost or last section, with each mast section being locked to the one outside it.

Thus, the present extensible support is composed of many telescoping sections which can be raised or lowered automatically by means of a mechanism which is located entirely in the outermost section. A pneumatic cylinder lifts the innermost section with the longest travel into latching position in a single stroke and then successively hitches up the next outer sections with the previously lifted ones latched to them. Thus one uses the yet to be lifted sections as a support for the one being lifted. With the present construction, special seals and valves are not required between the adjacent sections and it is not necessary to pressurize the inside of the support. Accordingly, construction and maintenance costs are kept to a minimum. Moreover, the

subject support can be extended and retracted very quickly and easily by a single person. All that is required is a source of air under pressure, such as a manual or battery-operated pump.

The spider and latch mechanism on each section to be described later performs a dual function in that it facilitates raising or lowering each mast section in the proper sequence. Also, it locks each section in place either at the top of the next outer section when the mast section is being extended, or at the bottom thereof if the mast is being retracted. Yet the fixture itself is reliable so that the raising and lowering operations are essentially trouble-free.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an isometric view with parts broken away of a telescoping mast embodying the principles of the present invention, with the mast shown in its fully retracted condition;

FIG. 1A is a view similar to FIG. 1 showing the mast in its fully extended condition and also showing in block diagram the elements required to operate the mast;

FIGS. 2A-2E are diagrammatic views illustrating how the mast is extended and retracted in use;

FIG. 3 is an isometric view on a larger scale and with parts broken away showing in greater detail the extending and retracting mechanism in the FIG. 1 mast;

FIG. 4 is an exploded isometric view on a still larger scale showing in greater detail the spider and latch mechanism which facilitates raising and lowering the mast sections;

FIG. 5 is a fragmentary elevation view of a mast section and the FIG. 4 mechanism therein; and

F IGS. 6A-6G are diagrammatic views illustrating the operation of the FIG. 4 mechanism at different points in the operating cycle of the mast.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 1A of the drawings, the subject mast is composed of a number of similar telescoping sections. For ease of illustration, we have shown only three such sections. These are identified as the first or innermost section 10a, the second or middle section 10b and the third or outermost section 10c. Obviously, however, any number of sections may be used depending upon the particular application. The lower end of the third section is secured to a discoid base 12 which includes three or more depending legs 14 which are arranged to engage the ground.

When the mast is in its retracted position shown in FIG. 1, the three mast sections are all nested together adjacent base 12. The load, in this case an antenna indicated generally at 16, is secured atop mast section 10a. Antenna 16 includes a depending post 22 which is received in a sleeve 24 projecting up from the end of mast section 10a. The antenna is locked in place by means of a pin 26 which extends through registering openings in the post 22 and in the opposite sides of sleeve 24. A suitable coaxial connector 27 is provided near the bottom of mast section 100 for electrically connecting the antenna 16 to an associated electrical device such as a radio receiver (not shown).

A quick disconnect type of air fitting 28 is installed in base 12. When it is desired to erect the mast, a regulated air source 32 including a valve 34 is connected by way of hose 36 to fitting 28. When valve 34 is turned on, the air causes mast sections 10a and 10b to telescope out, in turn, so that the mast assumes its fully extended condition shown in FIG. 1A. The same procedure is followed to retract the mast.

Guy rings 42 and 44 are secured at the tops of mast sections 10a and 100, respectively. Before the mast is extended, guys 46 secured at one end to these rings. Then, after the mast is fully extended, the other ends of the guys are anchored to the ground at suitable locations about base-l2 by stakes 48 or other suitable means. Thus, when the mast is fully extended, it remains quite sturdy.

Turning now to FIGS. 2A-2E, mast sections 10a and 10b are raised and lowered by means of a single moving means in the form of a pneumatic ram shown generally at 54 situated inside section 10a. Ram 54 includes a cylinder 56 and a piston element 58 which slides within cylinder 56 and divides the cylinder into upper and lower fiuidtight chambers 62a and 62b. The sliding piston element 58 is connected by way of a rod 64 to base 12 so that the entire ram 54 is supported within the innermost mast section 10a. 1

When air is supplied to fitting 28 (FIG. 1), 1), it is directed alternately to chambers 62a and 62b. When the air is fed to chamber 62b, cylinder 56 is driven downward so that it is contained entirely within mast section 10c. In this collapsed state the length of the entire ram is less than that of the outermost section 10c. On the other hand, when air is supplied to chamber 62a, cylinder 56 is driven upwards for a distance somewhat less than the length of mast section 100. Thus, in response to the incoming air, cylinder 56 reciprocates up and down relative to piston element 58.

A pair of hooks 66a and 66b are mounted on opposite sides of cylinder 56 near the bottom thereof. These hooks are biased outward. Also a special fixture 68 to be described in detail later is mounted near the bottom of each movable mast section, i.e., sections a and 10b, in line with one of these hooks. Fixtures 68 on mast sections 10a and 10b are situated on opposite sides of ram 54. Further, if the mast includes additional sections, the fixtures on the alternate sections are staggered by 180 so that they lie on opposite sides of ram 54. This assures that the mast sections are raised and lowered in the proper sequence.

Initially, when the mast is fully retracted as shown in FIG. 2A, a latch 72 which is part of each fixture 68 engages in an opening 74 in the next outer mast section near the bottom thereof. This locks all of the mast sections in their fully retracted condition shown in FIG. 2A when the mast is not being used. v

When air from source 32 (FIG. 1) is introduced into chamber 62a, cylinder 56 rises. One of the outwardly biased hooks, i.e., hook 66a, engages the opposing fixture 68 on the innermost mast section 10a. Continued upward movement of the cylinder causes the fixture 68 to withdraw latch 72 from opening 74 in mast section 10b so that mast section 10a is free to move upward relative to sections 10b and 100 along with cylinder 56.

When section 10a nears'its upper limit of travel as shown in FIG. 2B, the latch 72 engages in an opening 76 near the top of mast section 10b so that section 10a is locked in this elevated position. Air is then exhausted from chamber 62a and introduced into chamber 62b, causing cylinder 56 to return to its lower position as shown in FIG. 2C.

Cylinder 56 immediately commences another upstroke so that the other hook thereon, i.e., hook 66b, engages the opposing fixture 68 on the next outer mast section 10b. As before, the upward movement of the hook causes the fixture 68 to withdraw an associated latch 72 from opening 74 in mast section 100 so that mast section 10b (as well as mast section 10a) can be hitched up by cylinder 56. When section 10b nears its upper limit of travel as shown in FIG. 2D, the latch 72 therein engages in an opening 76 near the top of mast section 10c so that section 10b is locked in place atop section 10c and the mast is fully extended.

Finally, cylinder 56 returns to its lowermost position as shown in FIG. 2E and the air valve 34 (FIG. 1A) is shut off to complete the cycle. At this point, the guys 46 are anchored to the ground to reinforce the mast as shown in FIG. 1A and the unit is ready for use.

Still referring to FIGS. 2A-2E, the same procedure is followed to retract the mast. That is, air is introduced into cylinder 56, causing it to reciprocate up and down within mast section 10c. Initially, the mast sections are arranged as shown in FIG. 2E. Near the end of the first upstroke of the cylinder, the hook 66b engages the fixture 68 on mast section 10b. This engagement occurs slightly before cylinder 56 reaches its upper limit of travel. Since section 10b is locked against further upward movement, this limited upward movement of cylinder 56 causes fixture 68 on mast section 10b to retract its latch 72 from opening 76 in mast section 100.

Accordingly, when cylinder 56 commences its downward stroke, it lowers section 10b (as well as section 10a) back toward base 12.

When section 10b nears its lower limit of travel, the latch 72 thereon reengages in the opening 74 at the bottom of mast section 10c so as to lock section 10b in its retracted position as shown in FIG 2C.

Cylinder 56 then moves upward to retrieve the mast section in the same way as shown in FIG 2B. That is, hook 66a engages the fixture 68 on the mast section 10a, causing its latch 72 to retract from opening 76 in mast section 10b. Accordingly, mast section 10a is free to return to base 12 along with cylinder 56 as shown in FIG. 2A. At this point, the latch 72 again locks in the opening 74 in the mast section 10b, thus completing the retraction cycle.

Still referring to FIGS. 2A-2E, relatively wide bearing rings 78 are provided between the adjacent mast sections in order to insure that the sections slide properly relative to one another. Thus, in the illustrated embodiment, rings 78 are secured to mast sections 10b and 100 and are made of a material having a low coefficient of friction such as polytetraflouroethylene. The rings also function as stops for latches 72 and so limit the upward travel of the mast sections.

Preferably, each movable mast section, i.e., sections 10a and 10b and piston rod 64 includes a key (not shown) on its outer surface which rides in a keyway (not shown) in each bearing ring 78 and the inside wall of cylinder 56 respectively. These prevent the cylinder 56 and the mast sections from rotating relative to one another and so maintain the proper alignment between the hooks 66a and 66b, the fixtures 68 and the locking openings 74 and 76.

Turning now to FIG. 3, piston rod 64 is actually composed of two concentric inner and outer pipes 64a and 64b, respectively, both of which are butt welded to base 12. The air fitting 28 which is coupled to the air supply is connected by way of a tube 82 to the interior of pipe 64a. On the other hand, pipe 64b (i.e., the portion thereof outside of pipe 64a) is connected via a tube 84 to a vent fixture 86 mounted on the outside of mast section 100 near the bottom thereof.

A conventional, two-position air valve (not shown) is mounted inside piston element 58. When the valve is in one position, it connects the air inlet pipe 64a to a passage 88 exiting at the upper surface of piston element 58 and also connects the air outlet pipe 64b to a passage 92 exiting at the lower surface of element 58. Thus, with this position of the valve, air is introduced into cylinder chamber 62a while chamber 62b is vented so that the cylinder 56 is pushed upwards relative to piston element 58.

On the other hand, when the valve is in its other position, the air inlet pipe 64a is connected to passage 92 while the outlet pipe 64b is connected to passage 88 so that air is forced into the lower cylinder chamber 62b while the upper chamber 62a is vented so that the cylinder 56 moves down relative to element 58.

Conventional snap action push rods 94 and 96, projecting from the top and bottom of piston element 58 respectively control the position of the valve. More particularly, on the downstroke of cylinder 56, depression of rod 94 by the upper end wall of cylinder 56 switches the valve so that air is introduced into chamber 62a whereupon the cylinder commences its upstroke. At the end of the upstroke, depression of rod 96, by the lower end wall of the cylinder switches the valve so that the air is fed to cylinder chamber 62b whereupon cylinder 56 moves down again. Thus, as long as air is fed to fixture 28, the cylinder 56 reciprocates up and down on piston rod 64 inside the mast section 100.

Still referring to FIG. 3, the lifting hooks 66a and 66b are mounted in recesses 102a and 102b on opposite sides of cylinder 56 near the bottom thereof. Each hook has a relatively long shank 104 which is swingably connected at its upper end 104a to a fixture 106 secured to the cylinder wall. A torsion spring 108 is clamped to the cylinder wall underneath each hook shank 104 by brackets 110 affixed to the cylinder wall. Spring 108 includes a sideways extending end portion 108a which engages under hook shank 104 and the spring tends to unwind so that portion 108a pushes outwardly against the shank. Thus, each hook 66a and 66b is biased outward into contact with the inner wall of the nearest mast section, e.g., section 100 in FIG. 2B, section b in FIG. 2D and section 10c in FIG. 2E.

Unless the hook 66a or 66b actually engagesa fixture 68, it simply slides up and down on the inside wall of the adjacent mast section as the cylinder 56 reciprocates up and down. Thus, in FIG. 2B, while the hook 66a engages the fixture 68 in mast section 10a, hook 66b on the opposite side of the cylinder encounters no fixture and remains inactive. On the other hand, when hook 66b engages the fixture 68 on mast section 10b as shown in FIG. 2D, hook 66a is inactive.

Turning now to FIGS. 4 and 6A-6G, fixture 68 comprises a rotary spider 122 having four differently shaped cutouts 124, 126, 128 and 132. The shapes of these cutouts are difficult to describe in precise geometric terms. Therefore, we will describe them later in terms of their function when discussing the operation of the fixture.

The latch 72 discussed previously is a generally L- shaped member having a leg 72a and a tapered, slightly curved shank 72b. The latch is normally positioned under spider 122 as shown in FIG. 5 so that its leg 72a projects into cutout 126 and the shank end 720 projects into cutout 132. Of course, the rear face of the spider is recessed to accommodate the latch. A holding member 134 extends across the mouth of cutout 126 and is secured to the spider so as to hold the latch in place and prevent it from cocking. Latch 72 is free to pivot about its shank 7212 so that its leg is either nested within cutout 126 as shown in FIG. 6B or projects out of the cutout 126 (i.e., perpendicular to the plane of spider 122) as shown in FIG. 6A.

A generally L-shaped hook retainer 136 is also recessed under the spider 122 in much the same manner as latch 72. Hook retainer 136 includes a leg 136a and a tapered, slightly curved shank 136b. Retainer 136 is positioned so that its leg projects into cutout 124 and its shank end 1366 projects into cutout 132 so as to underlie shank end 72c of latch 72.

Hook retainer 136 is also free to rotate about its shank l36b between a first position wherein its leg 136a extends over towards the end 124a of cutout 124 as seen in FIG. 5, and a second position wherein the leg is swung over towards the right-hand end 124b of cutout 124 as seen in FIG. 6A. When the retainer 136 is in its first position, it locks the hook 66a or 66b FIG. 3) to fixture 68 when the associated mast section is being lowered. When it is in its second position, it provides bias for latch 72. The specific operation of retainer 136 will be discussed later in detail.

Each spider 122 with its associated latch 72 and retainer 136 is rotatively mounted on a relatively long, generally rectangular strap 138. More particularly, a pin 142 extends through a central opening 144 in the spider and thence through a second opening 146 in the middle of strap 138 where it is permanently secured so that the spider is free to rotate on the pin. Also, a generally L-shaped leaf spring 148 is secured by its short leg 148a to the strap just above the edge of spider 122. The long leg 148b of spring 148 extends down underneath the spider alongside strap 138 to a point slightly beyond the pivot opening 146 in the strap. When the spider is properly mounted, the latch 72 and retainerl36 are held in place between the spider and the strap 138 and spring 148, yet they can rotate on their respective shanks as described above. Latch 72 and hook retainer 136 are capable of pivoting each other through an angle of about when either one is forced to pivot during the operating sequence.

Spring 148 bears up against the retainer 136 to bias that member at certain points in the extension and retraction cycles of the mast as will be described later. Also, it prevents spider 122 from rotating in the wrong direction, i.e., clockwise, by engaging its sharp leg end 1480 against the edge of the cutout 126.

Referring to FIG. 5, fixture 68 is mounted on the inside wall of each movable mast section, e.g., section 10a near the bottom thereof. A circular opening 152 whose diameter is slightly larger than the diameter of spider 122 is formed in the wall of the mast section to receive the spider which projects out slightly from the section. Strap 138 is secured to the mast section in the usual way by screw or rivets 154.

The operation of the mast, and particularly the fixture 68, is shown diagrammatically in FIGS. 6A-6G.

All of the fixtures 68 operate in the same manner. Ac

cordingly, we will describe in detail only the operation of the fixture 68 on mast section 10a as that section is raised to its fully extended position, and then as it is lowered to its fully retracted position. The remaining mast sections are raised and lowered in exactly the same way, except that, as mentioned previously, the lifting hooks 66a and 66b are used alternately.

The FIGS. 6A, 6B, etc., each consists of diagrammatic front and side views of the fixture 68 at different points in its operating sequence. For clarity, we have exaggerated the clearance between the various components. We will assume at the outset that the mast is in its fully retracted position shown in FIG. 1. At this point, each mast section is locked to the next outer mast section by the engagement of its latch 72 in the lower opening 74 in the next outer section and the relative positions of the different components of fixture 68 are as shown in FIG. 6A.

More particularly, each spider 122 is initially oriented so that its cutout 126 is positioned at about 7 oclock. Also, the latch leg 72a extends into opening 74 in the lower end of mast section 10b so that section is prevented from moving upwards. In this connection,

9 it should be noted that opening 74 is generally arcuate, as best seen in FIGS. 1 and 1A. Initially, leg 72a is engaged in its lower end 74a while the upper end 74b of the opening is empty.

At the same time, the curved shank end 720 is swung away from retainer 136 while that member is oriented so that its leg 136a extends toward the right-hand 'end 12% of cutout 124. Finally, with this orientation of the spider, cutout 128 presents a downwardly curved edge which is in position to engage hook 66a as that is carried up by cylinder 56 (FIG. 3). At this point, spider 122 is prevented from rotating the wrong way, i.e., clockwise, by spring end 1480 opposite the edge of cutout 126.

Assume that the operator now turns on valve 34 (FIG. 1A). Cylinder 56 and its hook 66a move upwardly, the latter engaging in cutout 128. As best seen in FIGS. 4 and 5, strap 138 has a tapered lower end edge 138a. As hook 66a moves upwards, it encounters edge 138a and is guided thereby along the side edge l38b of strap 138 into cutout 128 which is aligned with the strap edge 138b. At this point, section a is still locked against upward movement by the engagement of latch 72 in opening 74. Consequently, a torque is developed about pin 142 which rotates the spider counter-clockwise. This movement swings latch leg 72a against the side of opening end 740 (FIG. 1), causing the latch to pivot about its shank. The spider is able to rotate through an angle of about 90 until hook 66a has swung around against strap side l38b at a point above pivot pin 142. Now, hook 66a is above pin 142 and latch 72 has pivoted on its shank to an extent that its leg 72a is folded down into cutout 126. Thus, it is withdrawn completely from opening 74 as seen in FIG. 6B. Mast section 10a is now free to slide upwards within section 10b towards its fully extended position shown in FIG. 1A.

With latch 72 in this position, its shank end 72c is swung down against the shank end 136c of retainer 136. This, in turn, pivots the retainer so that its leg 136a bears down against the leaf spring 148. Consequently, the spring 148 exerts a moment on the retainer 136 which, in turn, exerts a moment on latch 72 which tends to pivot its leg 720 out of cutout 126 in the spider. However, this is prevented by the opposing wall of mast section 10b.

The elements of fixture 68 remain in these same positions until cylinder 56 nears its upper limit of travel and the latch 72 is brought opposite the upper opening 76 in mast section 10b. Opening 76 is similar to opening 74 except that it is curved in the opposite direction as is shown in FIG. 1. The latch leg 72a, being biased outwardly as just described, springs out into opening 76 as shown in FIG. 6C. Now its shank end 720 no longer bears down on retainer 136 so that the latter member is free to swing away from spring 148.

Cylinder 56 continues moving upwards for a short distance until push rod 96 (FIG. 3) engaged by the bottom end wall of cylinder 56, causing the cylinder to reverse its direction. Section 100 is now lowered along with the cylinder 56 and hook 66a until its latch leg 72a engages the bottom edge of the upper opening end 76a. The weight of mast section 10a and the upward force exerted by the edge of opening 76 constitute a force couple which rotates spider 122 approximately 90 to the position shown in FIG. 6D. This movement swings the cutout 128 around so that its mouth moves past the strap edge 138b against which the hook 66a is engaged, with the result that the hook is pushed out of the cutout. The hook (and cylinder 56) are now free to move down to hitch up the next mast section 10b in the same way.

It should be noted at this point that the arcuate shape of opening 76 is required to accommodate the movement of latch leg 72a when spider 122 is rotated under the weight of section 10a as aforesaid. In other words, at the point when hook 66a is released, latch leg 72a has been swung around so that it is engaged in the upper end 76a of opening 76, similar to the showing in FIG. 1A. This engagement securely locks mast section 10a atop section 10b. It also fixes the orientation of the spider for initiation of the retraction sequence to be described presently.

The operation of fixture 68 during the retraction sequency is shown diagrammatically in FIGS. 6D6G. When air is supplied to the mast cylinder 56, it reciprocates as described above. With the spider 122 in the position shown in FIG. 6D, its cutout end 124a is in position to engage the upcoming hook 66a which is guided toward the cutout by strap edges 138a and 1381;. Hook 66a continues to move upwards somewhat as cylinder 56 completes its upstroke. However, mast section 10a is prevented from following it because latch leg 72a engages against the upper edge of the upper end 76a of opening 76 (FIG. 1A). The resulting force couple rotates the spider 122 counterclockwise approximately until hook 66a engages the strap edge 138b above pivot pin 142 as seen in FIG. 6B. This swings the latch leg 72a against the side of opening end 76a, causing the latch leg to fold down into cutout 126 so that section 10a is now free to slide down inside section 10b. As before, when the latch 72 is pivoted thusly, it pivots retainer 136 about its shank so that the retainer bears against spring 148 which, in turn, exerts a moment via the retainer on the latch tending to cause the latch leg to spring out of cutout 126. However, this is prevented by the inside wall of mast section 10b.

In addition, with the retainer 136 positioned as shown in FIG. 6E, its leg 136a is swung toward and closes off cutout end 124a containing hook 66a. This effectively locks the hook in the cutout 124 so that when the hook moves downwardly along with the cylinder 56, it cannot escape from the spider. Consequently, the mast section 10a is lowered by the hook 66a in a controlled fashion.

Turning now to FIG. 6F, when cylinder 56 nears its lower limit of travel, the latch leg 72a is brought opposite the upper end 74b of opening 74 at the lower end of mast section 10b. At this point, the continuing downward motion of the cylinder exerts a force on leg 136a via hook 66a. The leg 136a exerts a moment on latch leg 72a via shank end 1360 and shank end 726, thus forcing the latch leg 72a into the opening 74. The resultant pivoting of the latch 72 releases retainer 136 so that its leg 136a is swung away from the cutout end 124a. This releases hook 66a from the cutout and the hook continues moving downward with the cylinder 56.

At this point, the push rod 94 (FIG. 3) is engaged by the upper end of cylinder 56 which initiates another upstroke of cylinder 56 and its hook 660. With this position of spider 122, the wide-mouthed, rounded cutout 132 therein is in position to engage hook 66a being guided upwards by strap edges 138a and l38b. However, since the mast section a is locked against upward movement by the engagement of latch leg 72a in opening 74, the upwardly moving hook 660 causes spider 122 to rotate counterclockwise again approximately 90 until it assumes the position shown in FIG. 6G. Now the mouth'of cutout 132 has been swung around adjacent strap edge l38b so that the upwardly moving hook 66a is pushed by the strap edge 138b out of cutout 132. The hook then follows the cylinder as that completes its upstroke and return to the base 12. Since the mast section 10a is the last section to be retrieved, the retraction operation is complete and the valve 34 is turned off as soon as cylinder 56 returns to base 12.

The arcuate shape of opening 74 accommodates the movement of latch leg 72a when spider 122 is rotated during this part of the sequence. Thus, when the hook 660 is released, leg 72a is engaged in the lower end 74a of opening 74 similar to the showing in FIG. 1. This locks mast section 10a in its retracted position and also locks spider 122 in the proper position for engaging hook 66a during the next extension sequence.

In other words, as seen from FIG. 6G, spider 122 is oriented as it is in FIG. 6A so that its cutout 128 is positioned to engage the hook when the operator desires to extend the mast again.

Thus, the mast described herein can be extended and retracted quickly and easily by a single operator. All that is required is a source of air under pressure. It is important to note also that the extension or retraction operations can be stopped at any point simply by turning off the air. Thus, the mast can be extended only partway if the situation warrants it. Then when the air is turned on again, The extension or retraction sequency will be picked up where it left off and be completed. Normally, it is not desirable to turn off the air while a particular mast section is actually in motion because this may disorient one of the spiders 122. However, even if this should occur, the situation is remedied simply by turning the air on again and eventually the condition will correct itself after one or more cyclings of cylinder 56.

The subject mast is also relatively easy and inexpensive to make and maintain. This is because the extension and retraction mechanism, i.e., piston 54, is located entirely in the lowermost mast section, its stroke being slightly less than the length of that section. This means that the mast does not have to be pressurized and no elaborate seals are required between the individual mast sections. Consequently, one can count on the mast having a relatively long, useful, troublefree life, even under adverse conditions and despite repeated cyclings. Furthermore, it presents a relatively lightweight compact package.

The hitch feed technique described above also has application for extending and retracting other structures composed of individual sections which are slidable relative to one another from a first position wherein they are arrayed side-by-side to a second position wherein they are extended relative to each other in more or less staggered fashion. For example, a plurality of rectangular panel sections stacked face-to-face may be automatically extended by a device such as moving means 54 to form a relatively long, continuous barrier extending vertically or extending horizontally. It will be understood that in the latter case, the moving means 54 would be oriented so that its stroke is horizontal. Thus, one may erect a relatively long wall or fence quite quickly using individual, slidable wall or fence sections.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described.

What is claimed is:

1. An extendible and retractable structure compriss A. a plurality of structural sections, all of approximately the same length, mounted 1. adjacent to each other, and

2. including a first section, at least one intermediate section and a last section, said last section being fixedly mounted and said other sections being mounted to be slideable in the direction of their length relative to each other and to said last section,

B. a fixture mounted on each slidable section near a first end thereof,

C. said last section and each of said intermediate sections being formed to define an opening located near a second end thereof, opposite said first end,

and

D. moving means 1. positioned adjacent to said first section, and 2. reciprocable along said direction between first and second positions with a stroke slightly less than said length, E. means carried by said moving means for joining onto that fixture on the then nearest structural sec- .tion when said moving means is at said first position so that said nearest section 1. is carried along as said moving means moves to said second position, and

2. slides relative to the next adjacent structural section toward a fully extended position relative thereto, and

F. each of said fixtures including means for engaging said opening in said next adjacent section when said nearest section reaches its fully extended position to lock said nearest section in its extended position while said moving means returns to said first position to commence moving the next adjacent section in a similar manner.

2. An extendible and retractable structure as defined in claim 1 wherein A. said structural sections are separate telescoping tubes, and

B. said moving means comprises a pneumatic ram 1. positioned inside the innermost tube,

2. whose length when collapsed is less than the length of the outermost tube, and

3. reciprocable along the axis of the tubes so as to raise each tube in turn to an extended position relative to the next outer tube.

3. An extendible and retractable structure defined in claim 1 wherein A. said moving means comprises a pneumatic ram including a cylinder, a piston, and a piston rod 1. said rod being connected to a base, and 2. said cylinder being mounted to reciprocate along said direction, and

B. wherein said means for joining comprises one or more hooks l. movably mounted on said cylinder, and 2. biased away from said cylinder toward said structural sections.

4. An extendible and retractable structure as defined in claim 3 wherein each fixture comprises A. a spider rotatable on a structural section, said spider having a portion thereof arranged to engage one of said hooks when said cylinder is moving toward said second position, and wherein each of means for engaging includes a latch mounted on said spider so that it can be projected into or withdrawn from the opening in the next adjacent section depending upon the orientation of the spider.

5. An extendible and retractable structure as defined in claim 4 wherein the opening in said next adjacent section is so located as to register with that latch on said nearest section when said nearest section is in its fully extended position relative thereto.

6. An extendible and retractable structure as defined in claim 4 wherein A. said spider includes an additional portion located to engage one of said hooks when said nearest section is in its fully extended position, and

B. said means for engaging also includes a retainer mounted on said spider, and movable to lock said hook to said spider when said spider has a selected orientation so as to enable said cylinder to return said nearest section to its original position beside said next adjacent section.

7. An extendible and retractable structure as defined in claim 6 in which said last section and each of said intermediate sections is formed to define an additionalopening located near said first end,, said. additional opening being in a position to engage the latch on that section now adjacent thereto.

8. An extendible and retractable mast comprising A. A plurality of telescoping tubular sections including a fixed, outermost section and a plurality of inner, moveable sections, all of said sections being arranged on a common axis,

B. a base affixed to an end of said outermost section for supporting the sections vertically,

C. a fixture mounted on each moveable section near the lower end thereof,

D. each section other than the innermost section being formed to define an opening in the wall thereof near the upper end,

E. lifting means I. supported by said base inside the innermost section,

2. reciprocable along said axis with a stroke slightly less than the length of said outermost section, and

14 3. having means thereon for engaging the fixture on each moveable section, in turn, as the lifting means reciprocates and hitching up such section to an extended position relative to the next outer section, and F. each of said fixtures including means for automatically latching each moveable section to the next outer section through the opening therein as its extended position is reached.

9. An extendible and retractable mast as defined in claim 8 wherein the lifting means comprises a pneumatic ram including a cylinder, a piston and a piston rod and having A. said piston rod connected to said base, and

B. said cylinder. moveable along said axis from a first position wherein it lies completely within said outermost section to a second position where it extends a substantial distance out of the top of said outermost section.

10. An extendible and retractable mast as defined in claim 9 wherein said means for engaging comprises at least one hook-like member A. hinged to said cylinder, and

B. biased outwardly from said cylinder toward an adjacent mast section.

11. An extendible and retractible mast as defined in claim 10 in which each of said fixtures includes A. a first portion for engaging said hook-like member when the associated mast section is being extended, and

B. a second portion for engaging said hook-like member when the mast section is being retracted.

12. An extendible and retractable mast as defined in claim 11 wherein A. there are two such hook-like members, one on each side of said cylinder, and

B. the fixtures on alternate mast sections are situated on opposite sides of said cylinder in the path of one of said hook-like members.

13. An extendible and retractable mast as defined in claim 11 wherein each of said fixtures comprises a rotary spider A. rotatively mounted in the wall of a movable mast section so as to be accessible from both sides thereof, and

B. formed to define a plurality of cutouts in its periphery defining said first and second portions.

14. An extendible and retractable mast as defined in claim 13 wherein said means for latching includes a latch member mounted on said spider and swingable from a first position wherein it is recessed in the spider to a second position wherein it projects outward toward the next outer mast section, the position of said latch member being determined in part by the orientation of said spider.

15. An extendible and retractable mast as defined in claim 14 wherein each of said means for latching also includes means for projecting said latch member through that one of said openings which is in the next outer mast section.

16. An extendible and retractable mast as defined in claim 15 wherein each opening is shaped to accommodate movement of the received latch member which occurs when its associated spider is rotated through a relatively large angle.

l 17. An extendible and retractable mast as defined in claim in which each of said sections other than said innermost section is formed to define an additional opening located near the bottom thereof and cooperating with said latch members for locking said sections in their retracted positions.

18. An extendible and retractable mast as defined in claim 14 and further including a retainer A. having a leg projecting into that cutout of said spider defining said second portion, and B. pivotally mounted on the spider so that it can swing between a first position wherein it blocks the mouth of said cutout defining said second portion when a hook-like member is engaged therein as the associated mast section is being retracted to a second position wherein it clears the mouth of said cutout defining said second portion so that said hook-like member is free to disengage from said cutout, the position of said retainer being determined in part by the orientation of said spider. 19. The extendible and retractable mast as defined in claim 18 wherein A. said latch member and said retainer on each of said fixtures have portions thereof which engage one another so that the swinging of one between its two positions tends to cause the other to swing between its two positions, and B. each of said fixtures also includes means for biasing its associated retainer so that it tends to swing its associated latch member from its first position to its second position when said latch member is brought opposite the opening on the next outer mast section. 20. An extendible and retractable mast as defined in claim 9 A. wherein said piston rod comprises first and second tubes, and B. further including 1. a valve located within said piston and connected to one end of each of said tubes, 2. means for connecting the other end of said first tube to a source of air under pressure, 3. means for venting the other end of said second tube to the atmosphere, and 4. actuating means connected to said valve for a. actuating said valve when the cylinder reaches said first position so that air from said first tube is introduced into said cylinder above said piston and air in said cylinder below said piston is exhausted through the other tube, and b. actuating said valve when said cylinder reaches said second position so that air in said first tube is introduced into said cylinder below said piston while air in said cylinder above said piston is vented to the atmosphere through said second tube whereby said cylinder reciprocates up and down between its two positions as long as air is supplied to said first tube. 21. A telescoping mast comprising A. a plurality of tubular sections, l. arranged concentrically, 2. slidable relative to one another along their common axis, and

3. one end of the outermost section being affixed to a support,

B. a fixture mounted in the wall of each slidable section near a first end thereof,

C. each of said sections other than the innermost section being formed to define an opening in the wall thereof near a second end thereof,

D. a ram arranged on said axis inside the sections,

said ram including 1. a cylinder,

2. a piston slidable inside said cylinder, and

3. a piston rod connecting said piston to said support, said cylinder being reciprocable on said piston toward and away from said support.

E. means mounted on the outside of said cylinder for engaging the fixture on the adjacent mast section when said cylinder is at one end of its stroke so that said adjacent section 1. is carried along as said cylinder moves toward the other end of its stroke, and 2. slides along said axis to a fully extended position relative to the next outer section, and F. each of said fixtures including means for engaging the opening in the next outer section when the former section reaches its fully extended position so as to lock the former section in that position while said cylinder returns to hitch up the next outer section in a similar manner. 22. A telescoping mast as defined in claim 21 further including means for introducing air into said cylinder first on one side and then on the other side of said piston so that the cylinder reciprocates along said axis.

23. A telescoping mast as defined in claim 22 wherein said means for introducing includes A. a pair of conduits extending from the outside of said cylinder into said piston, B. a valve within said piston, said valve having 1. a first position in which it connects one conduit to the cylinder above the piston and the other conduit to the cylinder below the piston, and

2. a second position in which it connects said one conduit with said cylinder below said piston and said other conduit to said cylinder above said piston, and

C. means for switching said valve between said first and second positions when the cylinder reaches the opposite ends of its stroke.

24. A telescoping mast as defined in claim 21 wherein the means for engaging comprises A. a hook mounted on an outside wall of said cylinder, and

B. means for biasing said hook outward away from said cylinder into engagement with an adjacent mast section.

25. a telescoping mast as defined in claim 24 wherein each fixture comprises A. a spider rotatably mounted in a wall of the associated mast section and having a first peripheral cutout arranged to engage a hook when said cylinder moves from its retracted position adjacent said support to its extended position away from said support.

26. A telescoping mast as defined in claim 25 wherein said spider has a second peripheral cutout arranged to engage said hook when said cylinder is moving from its extended position to its retracted position so that said cylinder lowers the associated mast section toward said support in a controlled fashion.

27. An extendible and retractable mast comprising A. a plurality of telescoping tubular sections arranged on a common axis,

B. a base connected to one end of the outermost section for supporting the sections in an upstanding position,

C. lifting means reciprocable up and down along the axis within the innermost section from a retracted position wherein it is situated substantially entirely within the outermost mast section to an extended position wherein it projects substantially above the outermost section, and

D. a fixture l. rotatably mounted in the wall of each movable mast section near the bottom thereof,

2. accessible from both sides of the wall, and 3. 'having a plurality of cutouts around its periphery,

a. one of said cutouts engaging a portion of said lifting means when that is moving to its extended position so that the mast section to which that fixture is attached is carried upward by said lifting means, and

b. another of said cutouts engaging a portion of said lifting means when that is returning to its retracted position so that the mast section associated with that fixture is lowered to said base.

28. An extendible and retractable mast as defined in claim 27 A. wherein each of said fixtures includes a latch member pivotally mounted thereon and swingable from a first position in which it is nested within yet another of said cutouts to a second position in which it projects toward the next outer mast section, and

B. wherein each of said sections other than said innermost section is formed to define an opening in its wall near the top thereof, each of said openings being located to receive the outwardly projecting latch member on the next inner mast section when that latch member is drawn opposite the opening as the associated mast section is lifted to an extended position by said lifting means, thereby latching that mast section in its extended position atop the next outer mast section.

29. An extendible and retractable mast as defined in claim 28 and further including means for biasing said latch member from its first to its second position.

30. An extendible and retractable mast as defined in claim 29 wherein said means for biasing includes A. a retainer swingable mounted on said fixture and having a portion thereof engaging said latch member, and

B. a spring which pushes against said retainer when said latch member is in its first position, thereby tending to swing said retainer so that said retainer urges said latch member toward its second position.

31. An extendible and retractable mast as defined in claim 30 wherein said retainer has a portion which locks said portion of said lifting means in said other cul 8 tout so that when said lifting means moves toward its retracted position, said associated mast section is lowered along with it in a controlled fashion.

32. An extendible and retractable mast as defined in claim 27 wherein each fixture comprises A. a strap mounted on the wall of a mast section,

B. a spider 1. rotatably mounted on said strap,

2. projecting through a wall opening in the mast section, and

3. formed to define the aforesaid plurality of cutouts around its periphery, I

C. a generally L-shaped latch including a leg, a shank and a shank end 1. pivotally mounted on said spider, and 2. swingable from a first position wherein its leg is recessed into one of the cutouts in the spider and a second position wherein its leg projects out from the spider toward the next outer mast section.

D. a generally L-shaped retainer including a leg, a

shank and a shank end 1. pivotally mounted on said spider,

2. swingable from a first position wherein its leg nests in and closes off one of the cutouts in the spider and a second position wherein its leg projects out from the spider inside the mast section to which the spider is attached, and

3. the shank ends of said latch and said retainer engaging one another so that when one of these members is swung between its two positions, the other member swings between its two positions, and

E. a spring exerting a bias on the retainer tending to swing said retainer from its second position to its first position when said latch is in its first position so as to bias said latch toward its second position.

33. An extendible and retractable mast comprising A. a plurality of slidable telescoping tubular sections including a fixed, outermost section and a plurality of inner moveable sections, all of said sections being arranged concentrically,

B. each of said sections other than the innermost section being formed to define an opening in its wall near the upper end thereof,

C. a supportive base attached to one end of said outermost section to position the sections vertically, D. a spider rotatively mounted in the wall of each slidable section near the bottom thereof, each said spider being accessible from both sides of the associated wall and having first, second and third cutouts around its periphery,

E. a generally L-shaped latch including a leg and a shank pivotally mounted on each spider and swingable from a first position wherein its leg is recessed into said first cutouts in the spider and a second position wherein its leg projects out from the spider toward the next outer mast section,

F. a generally L-shaped retainer including a leg and a shank pivotally mounted on each spider so that its leg projects into said second cutout therein and being swingable between a first position wherein its leg projects from the spider inside the associated mast section and a second position wherein its leg closes the mouth of said second cutout, said latch and retainer having shank ends which engage one another so that movement of said latch from its first position to its second position causes the retainer to move from its first position to its second position, and vice-versa,

G. a spring mounted inside each slidable mast section adjacent the spider thereon, said spring being mounted so as to push against said leg of said retainer when it is in its first position so as to bias, by way of said retainer, the associated latch from its first position to its second position,

H. a pneumatic ram including a cylinder, a piston slideably' mounted within said cylinder, and a piston rod fastened to said piston, said ram being mounted inside the innermost mast section along the axis thereof with said piston rod secured to the base,

1. means for supplying air under pressure to said cylinder on opposite sides of said piston, alternately, whereby said cylinder reciprocates up and down,

J. at least one hook pivotally secured to the outer wall of said cylinder and biased outward toward an adjacent mast section, said hook being positioned to engage said third cutout in said spider on the upstroke of the cylinder so that the mast section associated with that spider is lifted up along with the cylinder until the latch thereon is received in said opening in the next outer mast section so that the associated mast section is latched in an extended position atop the next outer section, thereby enabling the cylinder to return to the base to hitch up the remaining slidable sections in turn in the same fashion.

34. An extendible and retractable mast as defined in claim 33 wherein when each slidable mast section is in its extended position atop the next outer section, the spider thereon is oriented so that said second cutout is in position to engage a hook on the cylinder when that reciprocates so that on an upstroke of said cylinder, said hook engages said second cutout and rotates said spider so that said latch thereon is retracted from the opening on the next outer mast section whereby said each slidable section an be lowered along with said cylinder toward said base with said leg of said retainer being held in its first position by said latch to prevent said hook from escaping from said second cutout. 

1. An extendible and retractable structure comprising, A. a plurality of structural sections, all of approximately the same length, mounted
 1. adjacent to each other, and
 2. including a first section, at least one intermediate section and a last section, said last section being fixedly mounted and said other sections being mounted to be slideable in the direction of their length relative to each other and to said last section, B. a fixture mounted on each slidable section near a first end thereof, C. said last section and each of said intermediate sections being formed to define an opening located near a second end thereof, opposite said first end, and D. moving means
 1. positioned adjacent to said first section, and
 2. reciprocable along said direction between first and second positions with a stroke slightly less than said length, E. means carried by said moving means for joining onto that fixture on the then nearest structural section when said moving means is at said first position so that said nearest section
 1. is carried along as said moving means moves to said second position, and
 2. slides relative to the next adjacent structural section toward a fully extended position relative thereto, and F. each of said fixtures including means for engaging said opening in said next adjacent section when said nearest section reaches its fully extended position to lock said nearest section in its extended position while said moving means returns to said first position to commence moving the next adjacent section in a similar manner.
 2. including a first section, at least one intermediate section and a last section, said last section being fixedly mounted and said other sections being mounted to be slideable in the direction of their length relative to each other and to said last section, B. a fixture mounted on each slidable section near a first end thereof, C. said last section and each of said intermediate sections being formed to define an opening located near a second end thereof, opposite said first end, and D. moving means
 2. reciprocable along said direction between first and second positions with a stroke slightly less than said length, E. means carried by said moving means for joining onto that fixture on the then nearest structural section when said moving means is at said first position so that said nearest section
 2. slides relative to the next adjacent structural section toward a fully extended position relative thereto, and F. each of said fixtures including means for engaging said opening in said next adjacent section when said nearest section reaches its fully extended position to lock said nearest section in its extended position while said moving means returns to said first position to commence moving the next adjacent section in a similar manner.
 2. An extendible and retractable structure as defined in claim 1 wherein A. said structural sections are separate telescoping tubes, and B. said moving means comprises a pneumatic ram
 2. whose length when collapsed is less than the length of the outermost tube, and
 2. reciprocable along said axis with a stroke slightly less than the length of said outermost section, and
 2. said cylinder being mounted to reciprocate along said direction, and B. wherein said means for joining compRises one or more hooks
 2. biased away from said cylinder toward said structural sections.
 2. means for connecting the other end of said first tube to a source of air under pressure,
 2. slidable relative to one another along their common axis, and
 2. a piston slidable inside said cylinder, and
 2. a second position in which it connects said one conduit with said cylinder below said piston and said other conduit to said cylinder above said piston, and C. means for switching said valve between said first and second positions when the cylinder reaches the opposite ends of its stroke.
 2. accessible from both sides of the wall, and
 2. slides along said axis to a fully extended position relative to the next outer section, and F. each of said fixtures including means for engaging the opening in the next outer section when the former section reaches its fully extended position so as to lock the former section in that position while said cylinder returns to hitch up the next outer section in a similar manner.
 2. projecting through a wall opening in the mast section, and
 2. swingable from a first position wherein its leg is recessed into one of the cutouts in the spider and a second position wherein its leg projects out from the spider toward the next outer mast section. D. a generally L-shaped retainer including a leg, a shank and a shank end
 2. swingable from a first position wherein its leg nests in and closes off one of the cutouts in the spider and a second position wherein its leg projects out from the spider inside the mast section to which the spider is attached, and
 3. the shank ends of said latch and said retainer engaging one another so that when one of these members is swung between its two positions, the other member swings between its two positions, and E. a spring exerting a bias on the retainer tending to swing said retainer from its second position to its first position when said latch is in its first position so as to bias said latch toward its second position.
 3. formed to define the aforesaid plurality of cutouts around its periphery, C. a generally L-shaped latch including a leg, a shank and a shank end
 3. having a plurality of cutouts around its periphery, a. one of said cutouts engaging a portion of said lifting means when that is moving to its extended position so that the mast section to which that fixture is attached is carried upward by said lifting means, and b. another of said cutouts engaging a portion of said lifting means when that is returning to its retracted position so that the mast section associated with that fixture is lowered to said base.
 3. a piston rod connecting said piston to said support, said cylinder being reciprocable on said piston toward and away from said support. E. means mounted on the outside of said cylinder for engaging the fixture on the adjacent mast section when said cylinder is at one end of its stroke so that said adjacent section
 3. one end of the outermost section being affixed to a support, B. a fixture mounted in the wall of each slidable section near a first end thereof, C. each of said sections other than the innermost section being formed to define an opening in the wall thereof near a second end thereof, D. a ram arranged on said axis inside the sections, said ram including
 3. means for venting the other end of said second tube to the atmosphere, and
 3. having means thereon for engaging the fixture on each moveable section, in turn, as the lifting means reciprocates and hitching up such section to an extended position relative to the next outer section, and F. each of said fixtures including means for automatically latching each moveable section to the next outer section through the opening therein as its extended position is reached.
 3. reciprocable along the axis of the tubes so as to raise each tube in turn to an extended position relative to the next outer tube.
 3. An extendible and retractable structure defined in claim 1 wherein A. said moving means comprises a pneumatic ram including a cylinder, a piston, and a piston rod
 4. actuating means connected to said valve for a. actuating said valve when the cylinder reaches said first position so that air from said first tube is introduced into said cylinder above said piston and air in said cylinder below said piston is exhausted through the other tube, and b. actuating said valve when said cylinder reaches said second position so that air in said first tube is introduced into said cylinder below said piston while air in said cylinder above said piston is vented to the atmosphere through said second tube whereby saiD cylinder reciprocates up and down between its two positions as long as air is supplied to said first tube.
 4. An extendible and retractable structure as defined in claim 3 wherein each fixture comprises A. a spider rotatable on a structural section, said spider having a portion thereof arranged to engage one of said hooks when said cylinder is moving toward said second position, and wherein each of means for engaging includes a latch mounted on said spider so that it can be projected into or withdrawn from the opening in the next adjacent section depending upon the orientation of the spider.
 5. An extendible and retractable structure as defined in claim 4 wherein the opening in said next adjacent section is so located as to register with that latch on said nearest section when said nearest section is in its fully extended position relative thereto.
 6. An extendible and retractable structure as defined in claim 4 wherein A. said spider includes an additional portion located to engage one of said hooks when said nearest section is in its fully extended position, and B. said means for engaging also includes a retainer mounted on said spider, and movable to lock said hook to said spider when said spider has a selected orientation so as to enable said cylinder to return said nearest section to its original position beside said next adjacent section.
 7. An extendible and retractable structure as defined in claim 6 in which said last section and each of said intermediate sections is formed to define an additional opening located near said first end,, said additional opening being in a position to engage the latch on that section now adjacent thereto.
 8. An extendible and retractable mast comprising A. A plurality of telescoping tubular sections including a fixed, outermost section and a plurality of inner, moveable sections, all of said sections being arranged on a common axis, B. a base affixed to an end of said outermost section for supporting the sections vertically, C. a fixture mounted on each moveable section near the lower end thereof, D. each section other than the innermost section being formed to define an opening in the wall thereof near the upper end, E. lifting means
 9. An extendible and retractable mast as defined in claim 8 wherein the lifting means comprises a pneumatic ram including a cylinder, a piston and a piston rod and having A. said piston rod connected to said base, and B. said cylinder moveable along said axis from a first position wherein it lies completely within said outermost section to a second position where it extends a substantial distance out of the top of said outermost section.
 10. An extendible and retractable mast as defined in claim 9 wherein said means for engaging comprises at least one hook-like member A. hinged to said cylinder, and B. biased outwardly from said cylinder toward an adjacent mast section.
 11. An extendible and retractible mast as defined in claim 10 in which each of said fixtures includes A. a first portion for engaging said hook-like member when the associated mast section is being extended, and B. a second portion for engaging said hook-like member when the mast section is being retracted.
 12. An extendible and retractable mast as defined in claim 11 wherein A. there are two such hook-like members, one on each side of said cylinder, and B. the fixtures on alternate mast sections are situated on opposite sides of said cylinder in the path of one of said hook-like members.
 13. An extendible and retractable mast as defined in claim 11 wherein each of said fixtures comprises a rotary spider A. rotatively mounted in the wall of a movable mast section so as to be accessible from both sides thereof, and B. formed to define a plurality of cutouts in its periphery defining said first and second portions.
 14. An extendible and retractable mast as defined in claim 13 wherein said means for latching includes a latch member mounted on said spider and swingable from a first position wherein it is recessed in the spider to a second position wherein it projects outward toward the next outer mast section, the position of said latch member being determined in part by the orientation of said spider.
 15. An extendible and retractable mast as defined in claim 14 wherein each of said means for latching also includes means for projecting said latch member through that one of said openings which is in the next outer mast section.
 16. An extendible and retractable mast as defined in claim 15 wherein each opening is shaped to accommodate movement of the received latch member which occurs when its associated spider is rotated through a relatively large angle.
 17. An extendible and retractable mast as defined in claim 15 in which each of said sections other than said innermost section is formed to define an additional opening located near the bottom thereof and cooperating with said latch members for locking said sections in their retracted positions.
 18. An extendible and retractable mast as defined in claim 14 and further including a retainer A. having a leg projecting into that cutout of said spider defining said second portion, and B. pivotally mounted on the spider so that it can swing between a first position wherein it blocks the mouth of said cutout defining said second portion when a hook-like member is engaged therein as the associated mast section is being retracted to a second position wherein it clears the mouth of said cutout defining said second portion so that said hook-like member is free to disengage from said cutout, the position of said retainer being determined in part by the orientation of said spider.
 19. The extendible and retractable mast as defined in claim 18 wherein A. said latch member and said retainer on each of said fixtures have portions thereof which engage one another so that the swinging of one between its two positions tends to cause the other to swing between its two positions, and B. each of said fixtures also includes means for biasing its associated retainer so that it tends to swing its associated latch member from its first position to its second position when said latch member is brought opposite the opening on the next outer mast section.
 20. An extendible and retractable mast as defined in claim 9 A. wherein said piston rod comprises first and second tubes, and B. further including
 21. A telescoping mast comprising A. a plurality of tubular sections,
 22. A telescoping mast as defined in claim 21 further including means for introducing air into said cylinder first on one side and then on the other side of said piston so that the cylinder reciprocates along said axis.
 23. A telescoping mast as defined in claim 22 wherein said means for introducing includes A. a pair of conduits extending from the outside of said cylinder into said piston, B. a valve within said piston, said valve having
 24. A telescoping mast as defined in claim 21 wherein the means for engaging comprises A. a hook mounted on an outside wall of said cylinder, and B. means for biasing said hook outward away from said cylinder into engagement with an adjacent mast section.
 25. a telescoping mast as defined in claim 24 wherein each fixture comprises A. a spider rotatably mounted in a wall of the associated mast section and having a first peripheral cutout arranged to engage a hook when said cylinder moves from its retracted position adjacent said support to its extended position away from said support.
 26. A telescoping mast as defined in claim 25 wherein said spider has a second peripheral cutout arranged to engage said hook when said cylinder is moving from its extended position to its retracted position so that said cylinder lowers the associated mast section toward said support in a controlled fashion.
 27. An extendible and retractable mast comprising A. a plurality of telescoping tubular sections arranged on a common axis, B. a base connected to one end of the outermost section for supporting the sections in an upstanding position, C. lifting means reciprocable up and down along the axis within the innermost section from a retracted position wherein it is situated substantially entirely within the outermost mast section to an extended position wherein it projects substantially above the outermost section, and D. a fixture
 28. An extendible and retractable mast as defined in claim 27 A. wherein each of said fixtures includes a latch member pivotally mounted thereon and swingable from a first position in which it is nested within yet another of said cutouts to a second position in which it projects toward the next outer mast section, and B. wherein each of said sections other than said innermost section is formed to define an opening in its wall near the top thereof, each of said openings being located to receive the outwardly projecting latch member on the next inner mast section when that latch member is drawn opposite the opening as the associated mast section is lifted to an extended position by said lifting means, thereby latching that mast section in its extended position atop the next outer mast section.
 29. An extendible and retractable mast as defined in claim 28 and further including means for biasing said latch member from its first to its second position.
 30. An extendible and retractable mast as defined in claim 29 wherein said means for biasing includes A. a retainer swingable mounted on said fixture and having a portion thereof engaging said latch member, and B. a spring which pushes against said retainer when said latch member is in its first position, thereby tending to swing said retainer so that said retainer urges said latch member toward its second position.
 31. An extendible and retractable mast as defined in claim 30 wherein said retainer has a portion which locks said portion of said lifting means in said other cutout so that when said lifting means moves toward its retracted position, said associated mast section is lowered along with it in a controlled fashion.
 32. An extendible and retractable mast as defined in claim 27 wherein each fixture comprises A. a strap mounted on the wall of a mast section, B. a spider
 33. An extendible and retractable mast comprising A. a plurality of slidable telescoping tubular sections including a fixed, outermosT section and a plurality of inner moveable sections, all of said sections being arranged concentrically, B. each of said sections other than the innermost section being formed to define an opening in its wall near the upper end thereof, C. a supportive base attached to one end of said outermost section to position the sections vertically, D. a spider rotatively mounted in the wall of each slidable section near the bottom thereof, each said spider being accessible from both sides of the associated wall and having first, second and third cutouts around its periphery, E. a generally L-shaped latch including a leg and a shank pivotally mounted on each spider and swingable from a first position wherein its leg is recessed into said first cutouts in the spider and a second position wherein its leg projects out from the spider toward the next outer mast section, F. a generally L-shaped retainer including a leg and a shank pivotally mounted on each spider so that its leg projects into said second cutout therein and being swingable between a first position wherein its leg projects from the spider inside the associated mast section and a second position wherein its leg closes the mouth of said second cutout, said latch and retainer having shank ends which engage one another so that movement of said latch from its first position to its second position causes the retainer to move from its first position to its second position, and vice-versa, G. a spring mounted inside each slidable mast section adjacent the spider thereon, said spring being mounted so as to push against said leg of said retainer when it is in its first position so as to bias, by way of said retainer, the associated latch from its first position to its second position, H. a pneumatic ram including a cylinder, a piston slideably mounted within said cylinder, and a piston rod fastened to said piston, said ram being mounted inside the innermost mast section along the axis thereof with said piston rod secured to the base, I. means for supplying air under pressure to said cylinder on opposite sides of said piston, alternately, whereby said cylinder reciprocates up and down, J. at least one hook pivotally secured to the outer wall of said cylinder and biased outward toward an adjacent mast section, said hook being positioned to engage said third cutout in said spider on the upstroke of the cylinder so that the mast section associated with that spider is lifted up along with the cylinder until the latch thereon is received in said opening in the next outer mast section so that the associated mast section is latched in an extended position atop the next outer section, thereby enabling the cylinder to return to the base to hitch up the remaining slidable sections in turn in the same fashion.
 34. An extendible and retractable mast as defined in claim 33 wherein when each slidable mast section is in its extended position atop the next outer section, the spider thereon is oriented so that said second cutout is in position to engage a hook on the cylinder when that reciprocates so that on an upstroke of said cylinder, said hook engages said second cutout and rotates said spider so that said latch thereon is retracted from the opening on the next outer mast section whereby said each slidable section an be lowered along with said cylinder toward said base with said leg of said retainer being held in its first position by said latch to prevent said hook from escaping from said second cutout. 